Just like Counter-Strike, Day of Defeat began as a mod project built using the original Half-Life engine. It was released by the modding community in 2000, but it became popular enough that Valve picked it up (it was built in their engine, after all), tweaked it a bit, and did a full-on retail release with big dog Activision as a publisher.

Day of Defeat was a World War II first-person shooter that had no single-player campaign; the whole game was played online. Even though drivable vehicles were just starting to become popular in shooters at the time, Day of Defeat focused purely on infantry-based warfare, with players fighting on either the Allied side or the Axis side. There were several various classes—each with a different weapons loadout—including Rifleman, Machinegunner, and Sniper.

Day of Defeat was limited to two game modes. The first was a Domination-like mode where players would have to capture certain areas of the map by standing next to a flag. The other provided Objective-type goals, usually with one team on offense and one on defense. While ten years later, gamers pretty much expect standard FPS game types like Team Deathmatch, Free-For-All, and Capture-the-Flag, Day of Defeat arrived in an era when it was okay (though not necessarily preferable) to offer a smaller selection of game modes. It was more important that the included gameplay options worked well than that they provided variety. And DoD's gameplay definitely worked well.

Maps in the game were quite well-designed, with tactical gameplay in mind. While a far cry from the destructibility of most modern shooters, Day of Defeat had a few select areas where you could blast through walls to open up new paths. Knowing where these destructible walls were located could grant an advantage over newbie opponents.

While it would be maybe a bit of an exaggeration to call Day of Defeat a realistic shooter, it encouraged more realistic battle tactics. For example, there was a stamina bar that would drain when a player would run or jump, and running would cause you to bring your weapon down to your side. This prevented the unrealistic run-and-gun tactics so prevalent in most online shooters. More importantly, it discouraged the "bunny hopping" that people would try to do to make headshots difficult. (These moves also made players' avatars look like leaping fools, which would have stood in stark contrast to the gritty, serious atmosphere of the game.)

DoD incorporated some very interesting grenade tactics that are worth mentioning. Most shooters let you "cook" grenades by holding down the fire button, but Day of Defeat didn't allow you to do this. Instead, cooking grenades required a risky process: throwing the grenade at your feet, picking it up using the "use" key, and tossing before it exploded in your hands. While you were holding a primed grenade, you ran the risk of getting popped off by a clever sniper, which would cause you to drop your grenade and often take out two or three teammates with you. Yet cooking grenades was essential, because they had fairly long timers and your opponents could pick them up and toss them back at you. Another technique picked up by the community was a sprinting/jumping toss that would hurl a grenade at great speeds over great distances, often skittering across the ground. Both of these techniques required a bit of practice, but mastering them was key to being able to hold your own in DoD's community of highly dedicated players.

In fact, this was probably DoD's biggest draw: the community. DoD players were hardcore; being able to compete required a pretty big commitment. Unlike so many shooters that can be mastered in a few days, DoD had a learning curve that demanded dedication and patience. While the road to victory could be long and arduous, sticking it out could be quite rewarding.

While Day of Defeat lives on in Day of Defeat: Source, a complete rebuild of the game In Valve's Source engine, the new version just didn't have the sort of staying power that the original had. It was well-received in the beginning, but it didn't maintain the community that its counterpart Counter-Strike: Source has managed to. Perhaps this can be due simply to the fact that by the time DoD: Source released, people had grown tired of World War II as a game genre. When the original DoD came out, it still felt relatively fresh.

Regardless, Day of Defeat provided some great World War II-inspired gameplay, and will be remembered as one of the greatest World War video games of all time.